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Extensive salt marsh restoration is expected in the northern Gulf of Mexico over the next several decades, funded in part by settlements from the 2010 Deepwater Horizon oil spill. Understanding the ecological benefits of restored marshes over time is integral to setting appropriate restoration targets and performance criteria and in determining the restoration area needed to achieve desired restoration goals and offset quantified natural resource injuries. We present a method for quantifying anticipated ecological benefits associated with marsh restoration projects, particularly marsh creation or enhancement through the placement of dredged material, in the northern Gulf of Mexico. Using salt marsh vegetation (percent cover, aboveground biomass, and belowground biomass) and indicator faunal species (periwinkle snails and amphipods) as representative marsh community components, we used resource equivalency analysis (REA) to model projected ecological benefits over time and quantified total net project benefits for a hypothetical marsh creation project in Barataria Bay, Louisiana. Sensitivity analysis of the resulting model suggests that the recovery trajectories for each marsh component were the most important drivers of modeled restoration benefits and that model uncertainty was greatest for marsh fauna, which has limited data availability compared to marsh vegetation and high natural variability. Longer-term monitoring at restored restoration sites and/or targeted monitoring of older restoration projects would reduce variability in the recovery trajectories for the marsh community components examined in this case study and improve the reliability of the REA model for projecting benefits associated with salt marsh restoration.

Recovery following salt marsh restoration in the northern Gulf of Mexico is investigated using meta-analysis for two salt marsh indicator invertebrates, the periwinkle snail (Littoraria irrorata) and amphipod crustaceans (Amphipoda). These invertebrates serve key marsh ecosystem functions including facilitating nutrient cycling and serving as prey for larger ecologically and economically important species. Recovery of periwinkles in restored marshes compared to reference sites is quantified by progression in population density and, because the species is long-lived (~ 10 years), in terms of biomass added per unit area each year following restoration. Amphipods are shorter-lived with high annual turnover; thus, recovery through time is estimated by the density of individuals rather than by biomass. The results of the analyses indicate progressive periwinkle recovery to equivalence with reference systems by year 4 in terms of density and year 6 with respect to annual biomass addition, while amphipod densities do not fully recover in the first 20 years following restoration. Although periwinkle recovery in terms of annual biomass addition reaches equivalence by year 6, the development of an age class structure characteristic of reference marshes would likely take longer because of the relatively long lifespan for this species. In addition to providing insight into the benefits of salt marsh restoration in the northern Gulf of Mexico, the approach described can be applied more generally to restoration scaling in a natural resource damage assessment context.

[1] Particulate organic carbon (POC) export fluxes and net primary production (NPP) rates are used to assess seasonal patterns in the export ratio (e-ratio = POC export/NPP) in relation to proximity of the sea-ice edge near the shelf break of the eastern Bering Sea during 2008–2010. POC fluxes were relatively low in April (4.6 ± 1.6, trap, and 5.7 ± 4.3 mmol C m−2 d−1, 234Th-derived) and increased in May–early June (19.9 ± 13.3 and 17.0 ± 8.8 mmol C m−2 d−1). POC export reached a maximum in mid-June–mid-July (30.0 ± 12.6 and 48.1 ± 17.4 in 2009; 33.1 ± 27.6 and 57.0 ± 68.4 mmol C m−2 d−1 in 2010) and decreased by late July (13.1 ± 4.7 and 14.1 ± 8.0 mmol C m−2 d−1). NPP rates were relatively high and export fluxes low near the ice-edge in spring leading to e-ratios 1, which is attributed to a temporal decoupling, or offset, of spring NPP and export during summer. While these observations reveal a seasonal progression in POC export and the e-ratio, there is no direct relationship to sea-ice proximity. Furthermore, based on a water column-sediment 234Th budget, the off-shelf export of POC during spring-summer is estimated to be 24 ± 35 mmol C m−2 d−1, which represents an off-shelf e-ratio of 0.07 and 0.21 for contemporaneous seasonally averaged daily NPP and 0.17 and 0.52 for historical monthly averaged daily NPP. An implication is that off-shelf POC transport may represent a seasonal net sink for CO2 in this and other polar shelf regions.

Th abstract As part of the Bering Ecosystem Study-Bering Sea Integrated Ecosystem Research Program (BEST-BSIERP), distributions of 234 Th in the water column and sediments were measured at approximately 60 stations over the shelf and slope/oceanic regions of the eastern Bering Sea during spring and summer of 2009 and 2010. During this study period, the inventory of sediment excess 234 Th ( 234 Thxs) on the shelf was determined to be ∼1/3 of the total 234 Th deficit in the overlying water column; the average focusing factor (FFTh ¼sediment 234 Thxs/water column 234 Th deficit) was 0.3470.23. In addition, the export flux of 234 Th from the shelf to the slope/oceanic region was determined to be on average ∼30% of the total production of 234 Th throughout the shelf. Taken together, these results indicate that 234 Th and associated particles are largely retained on the shelf, and that shelf sediments represent a sink for particles. In contrast, the FFTh in the slope/oceanic region was higher, averaging 1.5271.34. The higher FFTh at the slope is attributed primarily to enhanced scavenging removal and sediment deposition of 234 Th associated with periods of high biogenic particle flux at the marginal ice zone during the spring sea- ice retreat. A more general conclusion is that the ocean margin of the eastern Bering Sea may serve as an accumulation area for particles and associated reactive chemicals.

Climate change in the circumpolar region is causing dramatic environmental change that is increasing the vulnerability of infrastructure. We quantified the economic impacts of climate change on Alaska public infrastructure under relatively high and low climate forcing scenarios [representative concentration pathway 8.5 (RCP8.5) and RCP4.5] using an infrastructure model modified to account for unique climate impacts at northern latitudes, including near-surface permafrost thaw. Additionally, we evaluated how proactive adaptation influenced economic impacts on select infrastructure types and developed first-order estimates of potential land losses associated with coastal erosion and lengthening of the coastal ice-free season for 12 communities. Cumulative estimated expenses from climate-related damage to infrastructure without adaptation measures (hereafter damages) from 2015 to 2099 totaled $5.5 billion (2015 dollars, 3% discount) for RCP8.5 and $4.2 billion for RCP4.5, suggesting that reducing greenhouse gas emissions could lessen damages by $1.3 billion this century. The distribution of damages varied across the state, with the largest damages projected for the interior and southcentral Alaska. The largest source of damages was road flooding caused by increased precipitation followed by damages to buildings associated with near-surface permafrost thaw. Smaller damages were observed for airports, railroads, and pipelines. Proactive adaptation reduced total projected cumulative expenditures to $2.9 billion for RCP8.5 and $2.3 billion for RCP4.5. For road flooding, adaptation provided an annual savings of 80-100% across four study eras. For nearly all infrastructure types and time periods evaluated, damages and adaptation costs were larger for RCP8.5 than RCP4.5. Estimated coastal erosion losses were also larger for RCP8.5.